Deleting known hosts in my Fritz!Box 7170 is a PITA. One click per host plus the wait for page reload. This is a script to take the P from ITA :p (untested in this form. todo: wait for DOM structure instead of fixed timeout)

fritzbox-delete-hosts.js

var
	pattern = /^PC-192/,
	deleteText = 'Löschen',
	timeout = 3000;

(function moo() {
	var found = Array.prototype.some.call(document.getElementsByTagName('frame')[0].contentDocument.querySelectorAll('button[value="' + deleteText + '"]'), function (e) {
		var hostname = e.parentNode.parentNode.firstChild.nextSibling.textContent.trim();
		if (hostname.match(pattern)) {
			console.log('deleting ' + hostname + '...');
			e.onclick();
			return true;
		}
	});
	if (found) {
		setTimeout(moo, timeout);
	} else {
		console.log('no further hosts found.')
	}
}());